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METHODS OF STUDYING THE RESPIRATORY EXCHANGE 



IN SMALL AQUATIC ORGANISMS, WITH PARTICULAR 



REFERENCE TO THE USE OF FLAGELLATES AS 



AN INDICATOR FOR OXYGEN CONSUMPTION. 



By H. MUNRO fox. 



(From the Laboratory of the Marine Biological Association, Plymouth, England, and 

 the Biological Laboratory of the School of Medicine, Cairo, Egypt.) 



(Received for publication, March 5, 1921.) 



The results described below are a sequel to those already pub- 

 lished in this Journal on the spontaneous aggregation of flagellates.^ 

 In that publication it was shown that a flagellate, Bodo sulcatus, 

 forms aggregations in regions where the concentration of dissolved 

 oxygen is an optimum for it. This optimum is less than the satura- 

 tion concentration of oxygen dissolved in water under atmospheric 

 partial pressure. The flagellates move out of regions where the 

 oxygen concentration is above or below the optimum to gather into 

 the optimal regions. They are positively chemotactic to a certain 

 concentration of dissolved oxygen. 



This behavior of the flagellates can be made use of to indicate 

 changes in the concentration of dissolved oxygen due to the respira- 

 tion of an aquatic organism present in the water. For if the organ- 

 ism under investigation be kept motionless in a suspension of the 

 flagellates in water saturated with oxygen at the atmospheric par- 

 tial pressure, the flagellates will collect into those regions where the 

 oxygen concentration is lowered through the respiratory activity 

 of the organism. The sizes of the aggregations of flagellates thus 

 formed will show the relative amounts of oxygen absorbed by the 

 different parts of the surface of the organism. 



The following experiment will show how the method is applied, 

 A small fresh water invertebrate, such as a Chironomus larva, is 



•»* ^ Fox, H. M., An investigation into the cause of the spontaneous aggregation 

 ^ of flagellates and into the reactions of flagellates to dissolved oxygen, J. Gen. 

 -- Physiol., 1920-21, iii, 483, 501. 

 -^ 565 



